A gas turbine engine generally includes a fan and a core arranged in flow communication with one another. Additionally, the core of the gas turbine engine generally includes, in serial flow order, a compressor section, a combustion section, a turbine section, and an exhaust section. In operation, air is provided from the fan to an inlet of the compressor section where one or more axial compressors progressively compress the air until it reaches the combustion section. Fuel is mixed with the compressed air and burned within the combustion section to provide combustion gases. The combustion gases are routed from the combustion section to the turbine section. The flow of combustion gases through the turbine section drives the turbine section and is then routed through the exhaust section, e.g., to atmosphere.
More particularly, the combustion section includes a combustor having a combustion chamber defined by a combustor liner. Downstream of the combustor, the turbine section includes one or more stages, for example, each stage may include a plurality of stationary nozzle airfoils as well as a plurality of blade airfoils attached to a rotor that is driven by the flow of combustion gases against the blade airfoils. The turbine section may have other configurations as well. In any event, a flow path is defined by an inner boundary and an outer boundary, which both extend from the combustor through the stages of the turbine section.
Typically, the inner and outer boundaries defining the flow path comprise separate components. For example, an outer liner of the combustor, a separate outer band of a nozzle portion of a turbine stage, and a separate shroud of a blade portion of the turbine stage usually define at least a portion of the outer boundary of the flow path. However, utilizing separate components to form each of the outer boundary and the inner boundary requires a great number of parts, e.g., one or more seals may be required at each interface between the separate components to minimize leakage of fluid from the flow path, which can increase the complexity and weight of the gas turbine engine without eliminating leakage points between the separate components. Therefore, flow path assemblies may be utilized that have a unitary construction, e.g., a unitary outer boundary structure, where two or more components of the outer boundary are integrated into a single piece, and/or a unitary inner boundary structure, where two or more components of the inner boundary are integrated into a single piece.
A unitary construction of the flow path assembly may be furthered by separating the turbine nozzle airfoils, which also may be referred to as stator vanes, from the outer boundary structure and the inner boundary structure. As such, the outer boundary structure and/or the inner boundary structure each may be constructed as a unitary structure or may be constructed together as a single unitary structure, with the nozzle airfoils inserted and secured during subsequent assembly. Separating the nozzle airfoils from the outer and inner boundary structures of the flow path assembly thereby may simplify manufacturing, as well as reduce internal stresses compared to flow path assemblies comprising nozzle airfoils that are integral with the outer and/or inner boundary structures. However, separating the nozzle airfoils from the outer and inner boundaries may introduce points at which, e.g., fluid flowing through the flow path can leak from the flow path or where the fluid flowing through the flow path can leak from the pressure side of the nozzle airfoils to the suction side of the nozzle airfoils. This latter form of leakage may be referred to cross-over leakage, and cross-over leakage, from the higher pressure side to the lower pressure side of the airfoils, can negatively impact engine performance.
Accordingly, improved flow path assemblies would be desirable. For example, a flow path assembly utilizing a flow of cooling fluid to form a fluid curtain across a nozzle airfoil to discourage cross-over leakage would be beneficial. Further, providing more than one source of cooling fluid to form the fluid curtain would be advantageous. Additionally, a flow path assembly receiving a flow of cooling fluid that provides cooling to a plurality of nozzle airfoils, at least one of an inner or an outer boundary of the flow path, and/or downstream components of the flow path would be useful.